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Thread: Holy Cow! Now that Prices have changed, Which Way Should I Proceed?

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  1. #1
    DIY Junior Member DEDon's Avatar
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    Default Holy Cow! Now that Prices have changed, Which Way Should I Proceed?

    I came here, last year and decided to wait until my 19 YO A.O.Smith actually fails. After a thorough tank flush and although the thermostat is all the way up to the limit, it still hasn't failed. I have a power vented unit in the basement and, after replacing the leaking pressure valve and doing a flush, it has no leaks and has enough hot water for two showers.
    I had shopped around the Net, last year, and had pretty much decided on another power vented unit from A.O.Smith. Of course, since I had to trash my old hard drive on the computer, I lost all of that information.
    I know that I do want a high efficiency power vent unit and NOT a tank-less unit.
    I surely would like to do this job myself so I may ask about the gas plumbing changes that are needed, if any in fact are needed. My hope is to find a new unit that matches up to the old unit in exterior dimensions and plumbing dimensions, as well, so that there will be little to do but shut off the gas, evacuate the plumbing, disconnect, connect the new and turn it on and fire it up. It shouldn't be THAT big a deal. Right?
    My current unit is a FPS--40--J00N010000, a 42K BTU Gas fired unit.
    I would like to move up to a larger volume unit, even there are only two of us living here.
    I'm open to suggestions and providing any additional information.
    While at Costco the other day, I noticed a Lenox Promo table and asked for literature. I haven't called for an estimate appointment because I would like to do this on my own or with a helper. Any suggestions or comments?
    Is it practical to consider more for a Hybrid or High Efficiency Unit, considering the relatively small amount of savings that I will realize by doing so?
    Thank you.

  2. #2
    In the trades Dana's Avatar
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    Do you need a bigger tank for the tub-filling capacity, or is it a running short on shower-water kind of deal?

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    DIY Junior Member DEDon's Avatar
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    Dana, thanks (a few months late)for the reply. I do need a bigger tank. The showers water doesn't stay hot, very long. I'm still using the old heater and it is getting closer to upgrade time (unit is just shy of 20 years old, now). The temperature setting on the unit is up all the way.
    Now, I have two more, living here. We're probably stressing the unit.

    It appears that I am going to have to go to another power vented unit because of location in the basement.

    I've been looking at A.O.Smith's 50gal Power Vented Unit. May I ask you for some suggestions, please?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What Dana was leading up to, was, if you have the room, a waste water heat recovery system could save the cost of a larger unit, and provide longer showers with the same sized unit. It has no effect when you're trying to fill a big tub, since there's no warm water going down the drain at that time. Rather than repeat all of that info, just do a search, it's been discussed a lot here. Also, assuming your prior thread was on this forum, it may easily still be here...the search function again to the rescue.

    In gas-fired WH, the two companies that seem to get the most stars are Bradford-White (you may have trouble buying one of these as they want it installed right, and tend to only sell to plumbers) and Rheem.

    The overall size of the units is likely going to be different, even for the same volume WH. The Feds mandated a vapor protection system for the burner that prevents it from igniting volatile gasses that may be in the area - gasoline fumes, solvents, etc. This typically has made the tanks somewhat taller. This may not be a huge problem IF your local codes allow flexible connections for the gas and water, the rigid connections almost never would line up.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    In the trades Dana's Avatar
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    Quote Originally Posted by DEDon View Post
    Dana, thanks (a few months late)for the reply. I do need a bigger tank. The showers water doesn't stay hot, very long. I'm still using the old heater and it is getting closer to upgrade time (unit is just shy of 20 years old, now). The temperature setting on the unit is up all the way.
    Now, I have two more, living here. We're probably stressing the unit.

    It appears that I am going to have to go to another power vented unit because of location in the basement.

    I've been looking at A.O.Smith's 50gal Power Vented Unit. May I ask you for some suggestions, please?

    It's highly likely that the reason you aren't getting the anticipated shower times out of the existing unit is that the dip-tube feeding the incoming cold water to the bottom of the tank has corroded and gotten much shorter, mixing the cold with the hot at mid-tank or higher. While this is a replacable part, it's not worth fixing a 20 year old hot water heater.

    Jim has it right- with a drainwater heat exchanger and a 42KBTU/hr 80% efficiency burner you can get "endless shower" performance during the summer/fall when the incoming water temps are warmer, and more than double the apparent-capacity of the tank during the winters. What you don't get out of it is "endless tub fill" performance, since to deliver the heat from the drain flow to the incoming water both the drain & hot water need to be running at the same time.



    If you upgraded to the condensing Vertex you'd have both a bigger burner, and more volume, but whether the upcharge would pay for itself in efficiency over hte anticipated lifecycle of the unit depends a bit on how much hot water you use, and your fuel costs. If you're on a natural gas main it might take a pretty sharp accounting pencil to figure that out, but if you're using propane it's a no-brainer- go for a condensing unit AND drainwater heat recovery.

    Drainwater heat recovery enhances the apparent efficiency as well as capacity, since it's taking heat that was literally going down the drain and returning it to the hot water tank. If you just swap out your existing unit with a comparable non-condensing unit and still don't have enough showering capacity, a drainwater heat exchanger will fix that. I suspect that with a shiny new unit that has a full-length dip-tube you'll be fine on showering capacity for a decade at least. At current natural gas prices drainwater heat recovery would probably take nearly a decade to pay for itself, but if it bumps north of $1.50/therm- delivered there's a reasonably short-term ROI on them. (If it keeps you from having to hear about it if your partner takes a shower right after you, the payoff is immediate! :-) )

    If you are heating your home with a hydronic boiler it may make more sense to install an indirect-fired hot water tank operated as a heating zone off the boiler instead of installing a standalone tank of any type. (It depends a bit on the boiler.)

  6. #6
    Master Plumber master plumber mark's Avatar
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    Cool Just want some information about this

    [

    Jim has it right- with a drainwater heat exchanger and a 42KBTU/hr 80% efficiency burner you can get "endless shower" performance during the summer/fall when the incoming water temps are warmer, and more than double the apparent-capacity of the tank during the winters. What you don't get out of it is "endless tub fill" performance, since to deliver the heat from the drain flow to the incoming water both the drain & hot water need to be running at the same time.



    Drainwater heat recovery enhances the apparent efficiency as well as capacity, since it's taking heat that was literally going down the drain and returning it to the hot water tank. If you just swap out your existing unit with a comparable non-condensing unit and still don't have enough showering capacity, a drainwater heat exchanger will fix that. I suspect that with a shiny new unit that has a full-length dip-tube you'll be fine on showering capacity for a decade at least. At current natural gas prices drainwater heat recovery would probably take nearly a decade to pay for itself, but if it bumps north of $1.50/therm- delivered there's a reasonably short-term ROI on them. (If it keeps you from having to hear about it if your partner takes a shower right after you, the payoff is immediate! :-) )


    Ok, I need to hear more about this drain water heat exchanger and what benefits it
    could provide....
    I read the link and it appears rather like something I dreamed up about 30 years ago... but never attempted because I could not see any payback or benefit...

    Why not loop some copper around the flu pipe on the water heater or on the furnace flu??

    better yet... Why not install a 30 gallon pre heating naked tank next to the heater..if you have the room.


    from what this fellow has presently, he probably ought to just get himself a
    50 gallon power vent and that will probably solve all his hot water problems without
    trying to break the bank... the extra 10 gallons is not gonna cost him but a few dollars a month more to heat and it will make the wife happy too......

  7. #7
    Master Plumber Caduceus's Avatar
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    RE: Drainwater heat exchanger.
    I would be surprised to see if this method of heat recovery has been approved by any plumbing code authorities. Though it is promoted by state and federal entities as a great 'green' resource, my understanding is that health departments and code enforcement agencies have not looked favorably towards them for a number of reasons.

    The main concern that I can see with this design is that a potable water supply pipe is in direct contact with a sanitary drain. This is a major plumbing 101 no-no. Both are made of a quality copper, but if ever there was a compromise between the pipes you would have a cross contamination problem. A variety of factors in any home in America could contribute to premature corrosion of the interior pipe walls and the 'human' factor must be recognized.

    Also, looking at the cost of the product and assuming it is installed as a DIY project to save money, I would think that your supply and drainage piping would have to be in an ideal design to keep the system efficient. If you have multiple stacks on different floors a lot of repiping and insulating may be required and a plumber would increase the costs.
    I have also looked at the cost recovery analysis for home owners and they seem to be over inflated. The same thing happened with tankless water heaters (and still is happening) where perfect lab environments didn't mimic real-life application and an inaccurate final analysis mislead the public. Tankless units were first said to show energy savings to recoup cost of installation in 5-7 years, now it is discovered that it may take 20-30 years to recoup the cost and the units typically don't last over ten years...can the same be said for drainwater heat exchanger systems? I don't know, but the green movement seems to love them and I guess time will tell.

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